NAGE 1

Question 1

Difference between a nucleoside and a nucleotide

Answer 1

Nucleoside = base + (deoxy) ribose
Nucleotide = base + sugar + phosphate`
Note that the base is attached C1

Question 2

Difference between thymine and uracil

Answer 2

thymine has methyl group attached to pyrimidine ring whereas uracil does not

Question 3

How are nucleotides linked together?

Answer 3

phosphodiester bonds 5’ to 3’ i.e. 3’OH of sugar is linked to phosphate group which is linked to 5’ OH of another nucleotide sugar

Question 4

Characteristics of DNA double helix

Answer 4

2nm wide
10bp per helical turn
right handed
antiparallel

Question 5

How many hydrogen bonds in A-T and G-C

Answer 5

G-C has 3 hydrogen bonds

A-T has 2 hydrogen bonds

Question 6

How to melt DNA? then reanneal?

Answer 6

Melt DNA using heat/ low salt

Reanneal by cooling/high salt

Question 7

What is chromatin?

Answer 7

A complex of DNA and proteins

Question 8

Describe the nucleosome

Answer 8

DNA wrapped around histone proteins causing a 7 fold condensation
Histone octamer consisting of 2A x 2, 2B x 2, 3 and 4
Linker DNA = 50bp
Core DNA = 150 bp
Histone 1 in between each nucleosome

Question 9

What comes after the nucleosome?

Answer 9

Further packaging to form the 30nm fibre. a 40 fold condensation

Question 10

What happens after the 30nm fibre?

Answer 10

Chromatin fibre is folded into loops causing a 100-1000 fold condensation and this is further packaged to give a chromosome which is a 10000 fold condensation

Question 11

What is a karyotype?

Answer 11

An organised profile of someone’s chromosomes

Question 12

Difference between ribose and deoxyribose

Answer 12

Deoxyribose is missing an oxygen atom in what would have been a hydroxyl group attached to C2 in ribose